FCC catalysts and additives have found their prolific use in petrochemical refining industries for improving the profitability of refiners. FCC catalysts are employed to crack low valuable petroleum crude oil comprising high boiling range, higher molecular weight hydrocarbon fractions to more valuable products such as LPG, gasoline and diesel. Since the introduction of zeolite based FCC catalysts in place of conventionally used acid-leached clays and artificial or natural silica-alumina catalysts, petroleum refining industries have observed a remarkable revolution in the designing and formulation of zeolite based FCC catalysts. Designing of the FCC catalysts based on different cracking process conditions and desired particular products have become the mainstay of the refineries.
Other than designing the FCC catalyst, use of different cracking catalyst-additives in combination with the FCC catalyst to obtain different products with varying properties and attributes has also been a point of great interest among research communities. For example, pentasil zeolite based additive is used for improving LPG and octane number of gasoline component. SOx additive is used for the reduction of sulfur emission, CO-Promoter additive is used for containment of CO emission while Bottom cracking additives are used for reducing bottoms.
In the case of LPG production, the use of cracking catalyst-additive plays an important role in boosting LPG production and/or to improve the octane number of gasoline, however, it also produces additional fuel gases, which may restrict the FCC operation due to reactor cyclone velocity limitation.
Further to this, the increased use of cheaper feedstocks i.e. heavy oil/resid/opportunity crudes also contributes towards production of more fuel gas.
This is because, in addition to the inferior cracking behavior of heavy feedstock, both metals and basic nitrogen compounds, which are known to poison FCC catalysts, are concentrated in the heavier end of gas oils, especially in the residuum. These poisons, present within large hydrocarbon molecules, deposit on the FCC catalyst, thereby deactivating the FCC catalyst and the additive. This results in production of more fuel gas and coke which ultimately lowers the overall conversion. The higher fuel gas yield often touches reactor cyclone velocity limits which results in lower severity operation of FCC unit, such as lower riser temperature. Similarly, higher coke yield leads to a higher regenerator temperature that lowers unit conversion.
Therefore, there is always felt a need to develop a FCC catalyst/additive system, which substantially lowers fuel gas production without affecting the general yield pattern of the cracking products thereby meeting the requirement of LPG, gasoline, diesel while lowering the undesirable bottom or clarified slurry oil (CSO).
U.S. Pat. No. 4,451,355 discloses a process for the conversion of hydrocarbon oil feed having a significant concentration of vanadium to light oil products in the presence of a cracking catalyst containing calcium compound such as calcium-titanium, calcium-zirconium, calcium-titanium-zirconium oxides and mixtures thereof. However, the scope of the process disclosed in U.S. Pat. No. 4,451,355 is limited to passivate the vanadium deposited on the catalyst during the catalytic cracking process and it is silent on the production of fuel gas.
U.S. Pat. No. 5,260,240 discloses a process for passivating the reactivity of nickel and vanadium in a cracking catalyst by adding a calcium-additive with the metal laden catalyst. The process employs an additive prepared from dolomite and sepiolite material for extracting vanadium and nickel from metal laden FCC catalyst in the presence of steam at high temperature. Calcium containing additive found to enhance the activity of cracking catalyst.
Escobar et al. (Applied catalysis A: General, vol. 339, (2008) 61-67) teaches the effect of calcium on coke formation over ultra stable Y zeolite catalyst in the absence and presence of nickel and vanadium metal. Different zeolite samples are prepared by impregnating nickel and vanadium on ultra stable Y zeolite, previously exchanged with calcium. The catalyst samples are used for cracking of n-hexane at 500° C. The study showed that catalyst containing Ca in combination with nickel and vanadium reduces coke formation and increases olefin to paraffin ratio.
Komatsu et al. (Applied catalysis A: General, vol. 214, (2001) 103-109) discloses the cracking of n-heptane on calcium exchanged ferrierite zeolite catalysts. Ca2+ exchanged ferrierite catalyst gives higher alkenes selectivity due to less secondary hydride transfer reaction from hydrogen-deficient species. It is also disclosed that the coke formation is suppressed on account of the presence of Ca2+ exchanged ferrierite.
Letzsch et al. (Oil & Gas journal, Nov. 29, 1982, 59-68) disclose the effect of alkali/alkaline metal contaminants like sodium, potassium, calcium and magnesium on FCC catalyst. The presence of sodium and potassium decreases the catalyst activity to a larger extent than calcium and magnesium for the cracking of cetane as model compound. The study however is silent on product selectivity with said modifications.
The present state of the art is silent on teaching the effect of calcium on product selectivity and its impact on fuel gas yield particularly in the absence of contaminant metals.
Therefore, the present invention is directed to the development of FCC catalyst component and additive component containing alkaline earth metals for cracking of a hydrocarbon feedstock, particularly in the absence of contaminant metals, for lowering the production of fuel gas without altering the cracking products yield.